Instead, the new findings suggest red cones materialize through a specific sequence of events orchestrated by retinoic acid within the eye. Similarly, low levels of the acid changed the retina's genetic instructions and generated red cones later in development. "There still might be some randomness to it, but our big finding is that you make retinoic acid early in development," Johnston said. Green and red cone cells are remarkably similar except for a protein called opsin, which detects light and tells the brain what colors people see. "That has implications for figuring out exactly how retinoic acid is acting on genes."
